The following show the results obtained by varying the size of the bars or wires forming the armatures:

Bars of various small diameters were used with results corresponding to those given in the above tables. It was evident that the size of the armature had very little effect upon the induced magnetism, or upon our testing induced currents. To determine this point, we made a series of determinations of the strength of the induced currents which resulted from the employment of armatures of various sizes. The results are contained in the following table:

This fact has an important bearing upon the practical construction of magneto-electric engines; for it seems that we can vary the size of magnetic revolving armatures, within large limits, to suit considerations of speed, &c., without affecting materially the induced currents, through

coils upon the limbs of horseshoe magnets, near the poles of which the armature revolves. The above tables show that there is a slight increase of magnetism as the bar heats. Preliminary tests showed that the increase was slow, but gradual, up to the temperature of dull red heat; then, as the bar was heated to the temperature of white heat, its magnetic susceptibility fell, and apparently became less as the temperature increased beyond that of white heat. On cooling, the bar quickly regained its normal magnetic state of susceptibility. Thus, the curve which represents such a change would rise nearly as a straight line, inclined to the axis of X at a slight angle, up to the point of dull red heat; then it would fall quickly, in nearly a straight line, to the point of white heat; rising quickly again to the point of dull red heat, forming a V-shaped inflection in the curve, and then falling again, in nearly a straight line, towards the axis of X. One of Thomson's reflecting galvanometers was used in the above experiments. The results of the above show that the heating of the armatures of a magneto-electric engine increases rather than diminishes its magnetic susceptibility.

IX.

A CONSPECTUS OF THE NORTH AMERICAN
HYDROPHYLLACEÆ.

BY ASA GRAY.

Presented, March 9, 1875.

TRIBUS I. HYDROPHYLLEÆ. Ovarium uniloculare: placentæ dilatatæ primum succulentæ loculum fere implentes, demum membranaceæ capsulam totam intus vestientes et liberæ, facie interiore seminiferæ. Corolla æstiva tione sæpius convolutiva. Stylus bifidus. Seminis albumen corneum.

* Genitalia exserta. Perennes, nunc biennes, foliis alternis.

1. HYDROPHYLLUM Tourn.

** Stamina corolla breviora: calyx post anthesin accrescens. Annuæ, foliis aut infimis aut omnibus oppositis.

2. NEMOPHILA Nutt. Calycis sinus dentibus reflexis appendiculati. Corolla calyce longior. Semina sæpius quasi carunculata.

3. ELLISIA Linn. Calyx exappendiculatus, corollam superans vel subæquans Semina nuda, pauca (quandoque 1-2 inter placentam et valvam abscondita!).

TRIBUS II. PHACELIEÆ Benth. Ovarium 1-2-loculare. Capsula loculicida: valvæ medio (aut stricte aut mediante semiseptorum) placentiferæ. Placentæ angustæ. Stylus bifidus, rarissime indivisus. Corolla æstivatione imbri

cata.

Folia omnia opposita, integerrima: cymæ scorpioidea: stylus apice bifidus: placenta breves, 2-spermæ, tenues, a semiseptis plerumque secedentes! 4. DRAPERIA.

**Folia præter infima alterna: stylus pl. m. bifidus. Caulescentes.
+ Sepala vel calycis segmenta conformia.

5. PHACELIA. Corolla decidua (P. sericea excepta), nec flava. Stamina æqualiter basi corollæ inserta. Cymæ vel quasi-racemi spicæve plus minus scor pioideæ.

6. EMMENANTHE. Corolla (flava vel ochroleuca, campanulata) subscarioso- vel marcescenti-persistens. Cæt. Phacelia.

7. CONANTHUS. Stamina inæqualia tubo corollæ longe infundibuliformis inæqualiter inserta. Flores terminales et alares, sessiles.

Sepala dimorpha; 3 exteriora maxima, cordata, reticulata; 2 interiora parva linearia. Cæt. Phacelice.

8. TRICARDIA.

*** Folia alterna, reniformi-rotundata, palmatiloba: stylus indivisus: ovarium glabrum. Inflorescentia racemiformis subscaposa.

9. ROMANZOffia.

* * * * Folia (alterna, integerrima) omnia radicalia, scapos unifloros fulcrantia: stylus apice bifidus.

10. HESPEROCHIRON.

TRIBUS III. NAMEÆ Benth. Ovarium pl. m. biloculare. Capsula loculicida: placentæ divisæ per semisepta valvis integris raro bisectis adnatæ. Styli 2. Corolla æstivatione imbricata. · - A præcedente stylis discretis corolla plicis semper destituta ægre distincta.

11. NAMA. Corolla infundibuliformis vel fere hyprocraterimorpha. Genitalia inclusa. Capsula membranacea, valvis integris, semiseptis placentas pluripolyspermas auferentibus. Herbæ vel suffruticuli, foliis integerrimis. 12. ERIODICTYON. Corolla infundibuliformis vel subcampanulata. Genitalia subinclusa. Capsula crustacea, loculicide dein septicide in semi-valvas seu cocca 4 uno latere aperta oligosperma fissa. — Frutices vel suffrutices, foliis rigidis dentatis.

TRIBUS IV. HYDROLEE Benth. Ovarium biloculare: placentæ magnæ fungosæ, multiovulatæ. Capsula marginicide septifraga, pl. m. bivalvis, nunc irregulariter rupta; valvis nudis placentis crassis prorsus in unicam septo tenui bimarginatam connatis axi relinquentibus. Corolla fere rotata, æstivatione imbricata. Styli 2. Seminis albumen carnosum. 13. HYDROLEA.

1. HYDROPHYLLUM Tourn.

§ 1. EUHYDROPHYLLUM. Rhizomatibus horizontalibus perennans calyx immutatus, sinubus (no. 5 subexcepta) nudis.

* Folia pinnatifida vel pinnatisecta: calyx hispidus.

Pedunculus petiolo sæpissime glomerulo brevior: antheræ brevioblongæ.

1. H. CAPITATUM Dougl. - Var. ALPINUM Watson, Bot. King, p. 249. Cæspitoso-subacaule; cymis magis evolutis quasi radicalibus.

Pedunculus petiolo sæpius folio longior: antheræ oblongo-lineares. → Folia caulina circumscriptione elongato-oblonga, 7-15-partita: cyma densæ.

2. H. MACROPHYLLUM Nutt. Hispidum, validum; calyce albohispido profunde 5-fido, lobis e basi lata subulatis; corolla albida semipollicari. Atlantic United States, chiefly west of the Alleghany Mountains.

3. H. OCCIDENTALE. Pubescens, nunc parce hispidum, 1-2-pedale; segmentis foliorum oblongis incisis vel paucilobatis obtusis; pedunculis gracilioribus; calyce 5-partito, lobis lanceolatis obtusiusculis; corolla 3-pollicari.-H. capitatum Hook. & Arn. Bot. Beech. p. 371; Torr. Bot. Whipp. p. 69, non Dougl.-Pacific States.

Var. WATSONI. Humile, pube molliore nunc cinerea; calyce parce hispido; cyma minus densa.-H. macrophyllum var. occidentale Wats. 1. c. pro parte. Utah, California.

Var. FENDLERI. Pube magis hirsuta vel hispida nec cinerea; segmentis foliorum ovato-lanceolatis acutis vel acuminatis inciso-serratis; pedunculo breviore; cyma laxiuscula. — Colorado, New Mexico. ✦✦✦✦ Folia caulina circumscriptione ovata, 3-5-partita vel secta.

4. H. VIRGINICUM Linn. - Atlantic United States to Alaska. ** Folia palmati- (5–7-) lobata: calycis sinus dentibus inconspicuis erectis quandoque appendiculati.

5. H. CANADENSE Linn. - Atlantic United States and Canada.

§ 2. DECEMIUM Raf. Bienne: calycis post anthesin modice accrescentis sinus dentibus reflexis appendiculati: stamina ultra corollam rotato-campanulatam minus exserta.

6. H. APPENDICULATUM Michx.

2. NEMOPHILA Nutt.

Ovula 8-24: semina 5-15: folia pleraque opposita, pedunculo elongato superata. Californica.

Semina subglobosa, lævia, caruncula papilliformi: corolla alba violaceo maculata.

1. N. MACULATA Benth.

Semina oblongo-ovalia, demum corrugata vel tuberculato-rugosa, caruncula decidua.

2. N. INSIGNIS Dougl. Foliis 7-9-partitis: corollæ læte cæruleæ plicis internis brevibus rotundatis apice liberis breviter hirsutis. 3. N. MENZIESII Hook. & Arn. Minor; foliis 3-9-fidis; corollæ dilute cæruleæ seu albæ fundo sæpius punctatæ vel maculatæ plicis angustis adnatis hirsuto-ciliatis. - N. Menziesii Hook. & Arn. Bot. Beech. p. 152 & 372, forma a. N. liniflora Fisch. & Meyer, Sert. Petrop. t. 8, forma majora flore cæruleo. N. pedunculata Benth.