December 1, 1898.] 



KNOWLEDGE. 



283 



If we take the term Phanerogamia to mean the higher 

 plants, in which the organs of reproduction are readily 

 distinguishable, we may again make two series : — The 

 Gi/m)iospen)is, in which the seeds are not enclosed in a 

 special case, and the Ani/iii.yienr.'y, in which they are so 

 protected. Our pine-tree belongs to the former section, 

 and the flowering plants to the latter. 



Among the Gymnosperms are included three groups : — 

 The strange (inetticea. (with the Eiilu-Jra recalling a "horse- 

 tail," and the weird Weln itsdiia of African 

 deserts, reminding us of nothing but a certain 

 coal- fossil), which we cannot now dwell on ; 

 CyctiJs, the beautiful feathery tropical plants 

 recalling the tree ferns in growth, which we 

 must refer to later on ; and Co«('/;;s,mcluding 

 the firs, pines and larches, the yew, the 

 cypress and the juniper. 



Restricting ourselves to our type, and omit- 

 ting all details as to the structure of the 

 vegetative part of the plant, we start with 

 the fact that the pine is a woody exogenous 

 tree, with persistent narrow leaves, and a 

 fructification in the form of Cous. 



A cone is only a prolongation of the axis 

 of a branch bearing numerous closely-crowded 

 leaves which differ from other leaves in form, 

 and carry the reproductive organs. The 

 cone-leaves, or " scales," are in fact sporo- 

 lihylls jnat as much as those of the Selaginella 

 spike, but are more closely set and more 

 specially modified for their particular func- 

 tion. In the species of the Silaiiinella we 

 examined we found that in the same cone 

 similar leaves might bear difierent kinds of 

 spore cases ; Maovsj'orayujia containing four 

 large Macmspores, or Microsporam/ia with a 

 number of little Microspores, also in groups 

 of four. In the pine we find the difierence 

 carried a step further ; these two kinds of 

 spores are developed on distinct cones. 



In Abiis e.rcelsii the young shoots in the 

 early spring bear groups of small cones (one- 

 half to one inch long) of a yellow -white 

 colour. A section with a knife along one of 

 these shows that each of the close-set scales 

 carries on its under side a double sporangium, 

 filled when ripe with pale yellow dust. This 

 dust consists of •' poUen-;irains," or Micro- 

 sporayiijiii. The quantity produced is incre- 

 dible, and at the time of ripening the air of 

 the pine woods is full of it, blowing in golden clouds before 

 the slightest breeze. The grains may fall so thickly as to 

 cover the surface of lakes in the neighbourhood, and may 

 be carried enormous distances by the wind. 



The reason for the great buoyancy of the pine pollen 

 will be found on examining some under the microscope. 

 The main part consists of a mass of protoplasm, covered 

 by a firm wall, but this is expanded at two points into a 

 pair of large inflated wings, forming round chambers 

 containing air. Examination with a higher power and 

 suitable staining will show that the spore does not consist 

 of a single cell. There is a portion cut off from the rest 

 by a curved wall, and each part contains a nucleus. In 

 other words, before the germinating activity of the pollen- 

 grain has commenced, it has a tendency, however slight, 

 to form a cell tissue, in fact, a " prothallus," as we found 

 to be also the case, in a somewhat greater degree, with the 

 microspore of Selaginella. 



Turning to the female cones, which are larger and of a 



deep red colour when young, we find that if one of the 

 scales is stripped ofi', it will be found to bear at its base, on 

 the upper or inner side, a pair of pale oval bodies, which 

 are the macrospnrattriia or ovules. In scales from ripe 

 cones these have become seeds, and each has a membranous 

 " wing," which assists its carriage by wind as do the air- 

 sacs of the pollen-grain. One cannot, however, see much 

 resemblance between these ovules and the Selaginella 

 macrosporangia, and there is no sign of the contained 



A. — Seed of AInes excelsa. b.— Fertile brancli of the same plant bearing male 

 tones, c. — Longitudinal section through one of the cones, showing the ilicro- 

 sporangia on the under sides of the Microsporophylls (leaves of the cone). 

 D. E. — Longitudinal and transverse sections of a SlicrosporophTll, showing the double 

 Sporangium on the under side of the leaf, with Microspores in the cavity. F. — A 

 Microspore ("pollen-grain") highly magnified. The central port-on contains Pro- 

 toplasm, and the nucleus which is subsequently active in fertilizing the egg-cell. 

 The small cell cut off above is the vegetative cell representing the Prothallus, 

 and the rounded side outgrowths are the accessory air chambers that assist in 

 dispersion of the pollen by wind. a. H — Fertile branches bearing female cones, 

 from the outside and in section, i. .i.— Scales of the cones in young and older stages, 

 seen from the inner side. Each carries a pair of ovules at the base. K. — Diagram- 

 matic section through a scale and ils ovule, showing the Inte:;ument, Micropyle, 

 Nucellus, Embryo-sac, and Ai'chegoaia. L. — Diagrammatic section of the apex of 

 an ovule showinj the same structures, with pollen-grains seated on the nucellus, and 

 sending down tlieir tubes to the Archegonia. M. — Longitudmal section of the base 

 of an ovTiliferous scale, drawn from an actual preparation, showing the same 

 structm-es, and the coiu-se of a pollen tube. 



macrospores. If any such correspondence is to be estab- 

 lished, it must be done by cutting thin sections through 

 them, longitudinally, and as near the middle plane aa 

 possible, for microscopic examination. What we find then, 

 is that the whole is composed of a soft cellular mass, which, 

 however, can be seen to consist of different tissues. 



The outer layers form a covering (^int-e'jununt) to an 

 inner oval cell-mass, the nucellus ; but at the lower ex- 

 tremity the integument is absent, leaving a little round 

 gateway, the micropyle. Lying in the nucellar tissue is, 

 again, an elongated structure, the embryo-sac, which 

 represents a macrospore. It develops within itself, even at 

 an early stage, a cellular tissue, called the •ndosperm, 

 which may be compared with the prothallus tissue of the 

 Selaginella macrospore. When we examine the dark 

 bodies lying near its lower end, we find in each a large, 

 nucleated eyy-cell, or oospherc, with a group of small cells 

 at the apex, that may well represent the neck-cells of an 

 archeiiimiwn . 



